Study On The Extrusion Process Of Pre-deformation ZK60 Magnesium Alloy

As the lightest metal structure material,magnesium alloy has attracted wide attention in many fields and has wide application.However,the hexagonal crystal structure of magnesium alloy results in poor formability at room temperature and insufficient performance,which restricts the further application of the materials.In this paper,the influence of pre-deformation process and hot extrusion process parameters on the dynamic recrystallization mechanism of the ZK60 magnesium alloy bars is studied,by means of microstructure observation(OM),scanning electron microscopy(SEM)analysis,X-ray diffraction(XRD)and electron backscattered diffraction(EBSD).Through controlling the extent of recrystallization,microstructure homogeneity and texture intensity,it is aimed to enhance plasticity of the extruded bars and to improve their comprehensive performance.The main results are as follows:(1)In the process of hot extrusion,dynamic recrystallization(DRX)occurs in ZK60 magnesium alloy,and after that the extruded bars show two typical structure forms consisting of fine recrystallization grains and coarse non-recrystallization grains elongated along the extrusion direction(ED).The DRX mechanism of extruded bars without pre-deformation is dominant by continuous dynamic recrystallization(CDRX).For extruded bars with pre-deformation,a large number of extension twins generated in the process of pre-deformation will provide favorable conditions for twin inducing dynamic recrystallization mechanism(TDRX),which plays an important role in the process of hot extrusion.(2)The suitable increase of pre-deformation temperature and pre-deformation degree can improve the degree of recrystallization and homogeneity of the extruded bars observably,and the basal texture intensity is reduced.With the various influence factors of finer grains,stronger texture and improvement of microstructural homogeneity,the strength and elongation of extrusion bars with pre-deformation process greatly increases,and the yield asymmetry decreases significantly at the same time,so theirs comprehensive performance gets improved outstandingly.(3)Extrusion process parameters have significant influence on microstructure of extrusion bars.With the increase of extrusion temperature,the dynamic recrystallization is more sufficient and the basal texture intensity gets reduced.However,excessive temperature may cause some recrystallization grains to grow up unduly and reduce the homogeneity of microstructure.The increase of extrusion ratio can enhance the recrystallization degree and improve microstructural homogeneity,meanwhile the basal texture is strengthened.When the extrusion temperature is 300 ? and extrusion ratio ? is 10,the strength and elongation of the materials increases with influence of the refinement of grain and the improvement of the microstructure homogeneity,so the comprehensive performance of the extruded bars is optimal.(4)The texture of extrusion bars without pre-deformation is made up of(0001)[10(?)0] texture and(11(?)?0)[(?)010] texture.Pre-deformation process cannot change the major component of the texture,but the texture density decreases markedly due to the generation of((?)011)[3(?)?01]?((?)012)[2(?)4] and((?)021)[2(?)?14] random texture,which make dispersion degree of texture increased and texture weakened remarkably.When extrusion ratio rises,the texture density will increase and the basal texture strengthen.(5)When the pre-deformation temperature is 350?,pre-deformation degree is 20%,meanwhile the extrusion temperature is 300 ?,extrusion ratio ? is 10,the extruded bars show optimal comprehensive performance,whose tensile strength is 363 MPa and elongation is 30.7%,meanwhile yield asymmetry decreases significantly.